Rotliegend Tight Gas Field Leer (Ostfriesland) Germany A Development with a Multiple Hydraulically Fractured Horizontal Well: Project Leer Z4 Sept. 19 th, 2006: Slide: 1/ 30 Michael Koehler Symposium Tight Gas Fields, EBN and TNO Geo-Energy, September 19 th, 2006, Utrecht, The Netherlands The Presentation is based on a German Paper by M. Koehler and F. Kerekes: DGMK 04/2006, Celle, Germany, ISBN 3-936418-48-9. Gaz de France PRODUKTION EXPLORATION DEUTSCHLAND GmbH
Outlines Gas Field Leer: General Introduction Project Leer Z4: Multiple Fractured Horizontal Well - Drilling - Well Completion - Perforation - Stimulation - Well Cleanup and Tracer Investigation Conclusions - General - Positive Experiences - Negative Experiences Sept. 19 th, 2006: Slide: 2/ 30 Development of Tight Gas Field with a Multiple Hydraulically Fractured Horizontal Well: Project LEER Z4
Germany Netherlands Leer Geological Basemap: NW-German and NE-Dutch Gas Fields Sept. 19th, 2006: Slide: 3/ 30
LEER Z3a LEER Z3 LEER Z2 4375 - Top Bahnsen 4350-4350 - Leer structure is located on the southern margin of the Permian Basin (Rotliegend, Wustrow- and Bahnsen-Member). Depositional Setting: Desert plain: Dominated by aeolian dunes, dry sandflats, and damp sandflats with occasional presence of deposits of wet sandflats and aeolian mudflats. 4400 - Top Wu 4425 - Top Wu 4375-4375 - Top Wu Proximal channels with coarse deposits with claystone intraclasts and channels (less mature composition). Sheetfloods and lake deposits. The reservoir can be sub-divided into five drying upward cycles. 4450-4400 - 4400 - Sub-units are assumed to be climatically driven by lake base level and ground water table fluctuations. Subsequent lateral move of facies belts. 4425-4425 - k v /k h = 1/10 vertical barriers and lateral facies boundaries Risk: Compartmentalization. Basin (North) Sept. 19 th, 2006: Slide: 4/ 30 Depth in m TVD Hinterland (South) Logging Sequence and Depositional Environment: Leer: Bahnsen- and Wustrow-Member
Core Permeability (in situ) in md.. k(in situ) 100. 10. 1. 0.1 0.01 0.001 Ostfriesland: Bedekaspel (Rotliegendes) Core Permeability (in situ (pws=680 bar(a) @4350 m TVD b. SS), pre de-salted) Permeability (>30 md) Low-Permeability (>0.100 --30 30 md) Tight Gas (>0.020 --0.100 md) Ultra-Tight Gas (0.001 --0.020 md) LEER Z2 Z 2 LEER Z3a Z 3a BEKA Well Z1 Z1 ENHA Well Z2 Z1 SIWO Well Z3 Z1 LEER Z3 Z 3 BLKI Well Z4 Z1 ENHA Well Z5 Z2 U-MR Well Z6 Z1 G-MR Well Z7 Z1 0.0001 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Porosity in % Sept. 19 th, 2006: Slide: 5/ 30 In-situ Permeability Distribution from Core Data: Leer Z2-Z3a and other Ostfriesland Wells
W Teufe [m] LEER Leer Z4 Breinermoor E 500 Quartär Tertiär 32 13 3/8 1000 1500 Oberkreide Saltdome Rhaude 2000 2500 Jura Unterkreide 9 5/8 3000 Keuper 3500 4000 Muschelkalk Buntsandstein 7 Heidberg-Dambeck-Member Bahnsen-Wustrow-Member (gas bearing Sandstones) 4500 5000 Rotliegend Karbon (Westfal C) Zechstein 4 1/2 Leer Block FWL GWC ~ ~4470m 4464 m 5500 0 500 1000 1500 2000 2500m Sept. 19 th, 2006: Slide: 6/ 30 LEER Z4: Drilling Path and Project Target West-East-Cross-Section: Structure Leer
W LEER Z4 E Base Zechstein LEER Z4 Block Rhaude Block Sept. 19 th, 2006: Slide: 7/ 30 Cross-Section on the Base of PreSDM Seismic (Depths) LEER Z4 Block: Zechstein/Rotliegend
N-Fault Length and Width: N/S: 3.9 km x E/W: 1.2 km Area: 4.7 km² Structural Dip: 4.5 ENE FWL Ref. Depth: 4420 m TVDss Exploration Lisense Reservoir Pressure: 680 bar LEER Z4 FWL Temperature: 150 C Gross Thickness: 78 m LEER Z3 Surface location LP Top Wustow LEER Z3a Production Lisense Net Thickness: 45 m Porosity: 9.7% Water Saturation: 34% Permeability: 0.020-0.150 md FWL : 4464 m TVDss GWC: 4450 m TVDss Structure Map Top-WU-Member Central Leer Block 0 250 500 750 1000 1250m Sept. 19 th, 2006: Slide: 8/ 30 LEER Z2 FWL S-Fault OGIP (P90, P50, P10): 3050, 4300, 5600 Mio. m³(vn) Reservoir Parameter: WU- & BA-Member Central Leer Block
N-Fault LEER Z2: 1971 Gas Rate = 1500-1000 m³(vn)/h @WHFP = 8-5 bar FWL Permeability = 0.020 md OGIP = 5 Mio. m³(vn) LEER Z4 Leer Z4 FWL Exploration License LEER Z3: 1978 Gas Rate = 1000-1500 m³(vn)/h @WHFP = 266-224 bar Permeability = 0.050 md OGIP = 150-200 Mio. m³(vn) LEER Z3 Surface location LP Top Wustow LEER Z3a Production License LEER Z3a (post frac): 1998 Gas Rate = 9 500 m³(vn)/h @WHFP = 440 bar Permeability = 0.150 md OGIP = 530-600 Mio. m³(vn) Structure Map Top-WU-Member Central Leer Block 0 250 500 750 1000 1250m LEER Z2 S-Fault FWL LEER Z4: 2005 Field History: Well History & Test Results Sept. 19 th, 2006: Slide: 9/ 30
W LEER Schematic Teufe View of Well Completion [m] LEER Z4 500 1000 1500 2000 2500 Quartär 1-33,0m 32" - 57,36m 85/8" - 135,3m 103/4" - 150,0m 1 4 1/2" SSSV Landing Nipple 2 4 1/2" Tubing Oberkreide String (4 1/2" - 12,6 lb/ft) 3 7" Prod. Packer Type "CUT TO REALEASE" 2 4 4 1/2" Top NO-GO Landing Nipple 5 Top Liner 133/8" - 1039,0m 95/8" - 2640,0m Jura Leer Z4 32 Tertiär 13 3/8 Unterkreide 9 5/8 Breinermoor Salzstock Rhaude E 3000 3500 4000 7" - 4602,0m 3-4513,0m MM 4-4544,0m 5 41/2" LK - 4547,0m Keuper Muschelkalk Buntsandstein 7 Rig Down after Well Completion Heidberg-Dambeck-Member Bahnsen-Wustrow-Member (gas bearing Sandstone) 4500 5000 41/2" - 16,9 lb/ft Liner zementiert Rotliegend Perforationen - 5065m - 5375m - 4911m - 5237m - 5536m Karbon (Westfal C) - 5622,0m - 5680,0m Zechstein 4 1/2 Leer Block FWL GWC ~ ~4470m 4464 m 5500 1935,58m 0 500 1000 1500 2000 2500m Sept. 19 th, 2006: Slide: 10/ 30 LEER Z4: Well Path: W-E-Cross Section of Leer the Structure
SW NE GR Phi Frac 5 Frac 4 Frac 3 Frac 2 Frac 1 Leer Z4 Near Top Wustrow Leer Z4: Seismic Section vs. Geomodel Reservoir Section Sept. 19 th, 2006: Slide: 11/ 30
W E GR bad Sept. 19 th, 2006: Slide: 12/ 30 Top Wustrow Frac 5 Frac 4 GWC FWL Frac 3 General Trend of Reservoir Parameter Porosity Frac 2 Result: Well Path (WU) = 680 m AH, Frac Distance = 155 m, Net-Thickness = 328 m AH, Porosity = 11.1%, Water Sat. = 31.9%, 3 Compartments (cutoffs: Phi>= 9%, Sw< 50%) Frac 1 better Successful application of LWDtools Estimation of fracture positions based on logging results Influenced by: Sub seismic faults and compartments. Optimum number of fracture stimulations: Local conditions, numerical simulation and literature. Limited access: short perforation length LEER Z4: Cross Section : W-E - Well Path with GR- and Porosity-Log together with Frac-Positions
6Dw 4Dw 2Dw 1Dw ½Dw Influence of Perforation Sections on Frac- Initiation (Dw= Well Bore Diameter) Reference: El-Rabaa (1989): SPE 19 720 (from Soliman (2004): SPE 86 992) El-Rabaa: L(Perfo) <= 4*Dw(max) Soliman: L(Perfo) ca.2 ft = 0.6 m L(Perfo) 10 SPF Perforation: 3 1 / 8 big holes Case with 3, 4 to 6 effective Perfo Tunnels ( ) 45 135 /45 - Phasing, 10 SPF: 8 Shots/ 360 20 Perforations / 2 ft d(perfo, hole) = 0.69 = 17.5 mm Sept. 19 th, 2006: Slide: 13/ 30 Expected Fracture Initiation and Propagation based on a 3 1 / 8 Perforation Gun
p = C q ρ Perfo ( 2 2 4 n C d ) 2 1 Injection fluid Perfo d Perfo p Perfo q Injection ρ fluid n Perfo C d d Perfo C 1 = Perforation Friction = Injection Rate = Fluid Density = Number of active Perforations = Form Factor f(erosion) = Perforation Diameter @Casing = Unit Factor Perforation Pressure Loss for limited Entry Fracture Treatment Based on sharp-edged orifice equation (Romero SPE 63009 and Shah, GRI-Paper) Big Hole with 3 1/8"-Gun 10 SPF Perforation 20 holes/2 ft Parameter Symbol Unit Low Case Most Likely High Case Hole Diameter d(hole) inch 0.56 0.56 0.56 mm 14.2 14.2 14.2 Phasing Deg. 60 60 60 Holes/360 1 6 6 6 Perforation Length L(Perfo) inch 1.87 1.87 1.87 mm 47 47 47 Effective Number of Holes N(holes) 1 3 4 6 Fluid Density Rho(fluid) kg/m³ 1 040 1 040 1 040 lb/gal 8.68 8.68 8.68 Injection Rate q(injection) m³/min 4.00 4.00 4.00 bpm 25.16 25.16 25.16 Injection Rate per Hole bpm/hole 8.39 6.29 4.19 Proppant Quantity m(prop.) tons 120 120 120 lbm 264 555 264 555 264 555 Discharge Coefficient Cd 0.89 0.89 0.89 Perforation Pressure Drop D(p,perfo) psi 1 856 1 044 464 bar 128 72 32 Sept. 19 th, 2006: Slide: 14/ 30 LEER Z4: Expected Perforation Friction
Noise Protection Wall CT-Frame Operations Test Equipment CT-Unit Blender Silos Pumps TCC & Labor Tanks Heater Sept. 19 th, 2006: Slide: 15/ 30 LEER Z4: Layout: Frac- and Test-Equipment
Principle Treatment Schedule: Data Frac 1 (Breakdown & SRDT 1) Mini Frac Data Frac 2 (SRDT 2) Main Frac Sept. 19th, 2006: Slide: 16/ 30 Remarks All fracture fluids will be marked with fracture individual tracers 1. Breakdown Initiation of a fracture Stable fracture propagation 2. Step Rate Down Test 1 Estimation of near well bore friction (perforation and tortuosity) Estimation of effective numbers of perforations (min. 3-4 big holes ) 3. Shut-in ISIP, fracture closure and reservoir pressure 4. Mini Frac Creation of a x-linked fracture Modelling of fracture propagation Leak-off behavior, erosions with x-linked gel and low conc. proppant stage (1-3 ppg) 5. Step Rate Down Test 2 Analog Step Rate Down Test 1 Recognition of differences 6. Main Frac Based on the previous examinations LEER Z5: Treatment Schedule
5 1000 4 840 Step Rate Down Test BHP 1000 0.5 840 0.4 40 32 Frac-Dimensions Height 10 8 1 40 0.8 32 3 680 2 520 1 360 Fluid Efficiency WHP Slurry Rate 680 0.4 520 0.4 360 0.4 24 16 8 Length 6 4 2 0.6 24 0.4 16 0.2 8 0 0 Time 200 0 0 Time 0 0 0 Frac-Dimensions 200 Near Well Bore Friction 160 Totals Perfo Top Wustrow Sandstein 120 80 Perforation 0 Formation Breakdown Near Well Bore Friction effective Perforation Sept. 19 th, 2006: Slide: 17/ 30 6 12 18 24 32 Fracture Half Length 40 0 1 2 3 4 Pump Rate in m³/min Tortuosity LEER Z4: Data Frac 1: Breakdown Step Rate Down Test from Frac 4
Time Time Design of PAD volume to access securely the vertical fracture height. Investigation of erosion potential with x-linked gel and low concentrated proppant slugs. Perfo 1-2 slugs (prop. conc.: 1-3 ppg 120-360 g/l). Slug stages are placed to be effective after stabilization of fracture propagation. If two proppant slugs are pumped a sufficient buffer of x-linked gel is essential. General Leer problem: To initiate a fracture from a high stress regime to a low stress regime low fracture width @perforation. Sept. 19 th, 2006: Slide: 18/ 30 0 12 24 36 48 60 Fracture Half Length in m LEER Z4: Mini Frac: Example: Frac 4
LEGEND: SRDT 1 = Step Rate Down Test before Mini Frac. SRDT 2 = Step Rate Down Test after Mini Frac. High perforation friction before Mini Frac, even with big holes. Significant lower perforation friction after Mini Frac, due to erosion (x-linked gel and proppant slugs). Tortuosity is relatively low: Transverse fractures are expected (suitable well direction: ENE) Sept. 19 th, 2006: Slide: 19/ 30 Observed perforation friction and tortuosity LEER Z4: Comparison: Data Frac 1 und 2 of Frac 2 to Frac 4
Breakdown volume must be scheduled to reach a stable vertical fracture status, where a step rate down can be performed. The Mini Frac must be designed to reach the main vertical sequence and thus to examine the vertical stress profile. 1 slug test from 1-3 ppg should be sufficient. A step rate down test post Mini Frac should be performed as a standard to investigate the curability of the NWB friction. Sept. 19 th, 2006: Slide: 20/ 30 LEER Z4: Stimulation and Strategy Breakdown & STDT 1, Mini Frac and SRDT 2
5 on the fly -Coating Plateau @6 ppg: Begin on the fly -coating @50% proppant quantity. Smooth transfer to the next plateau. Plateau @8 ppg Tail of treatment: Problem with limited number of perforations Screenouts can occur. Frac 2-5 Perfo 120 t Pad volume according to stress profile and fracture dimensions, optional with slug stages. Smooth enhancement of proppant concentration to reach the first plateau phase with relatively constant proppant concentration. Sept. 19 th, 2006: Slide: 21/ 30 LEER Z4: Main Frac: Example: Frac 4
Trial with composite plugs: Temporarily plugged of with: Sand plug Frac 1 69.4 t Top Wustrow Porosity Frac 2 88.1 t GWC GR Frac 5 Frac 4 FWL Frac 3 Frac 2 Frac 1 Plugged-off with: Sand plug Trend Reservoir Parameter bad Frac 3 113.2 t better Plugged off: Sand plug auto-cleanout forced to set a new separate sand plug Frac 4 135.2 t All fractures are shown with the same fracture conductivity kf*wf scale in md.m @Fracture damage factor = 50%. Sandout = Sand plug Target fracture conductivity Sept. 19th, 2006: Slide: 22/ 30 Frac 5 1.5 t LEER Z4: Main Fracture Comparison: Frac 1 to 5
Proppants: 407 tonnes Clean Fluids: 2 618 m³ (during fracturing treatments) Total Injection: 3 172 m³ Sept. 19 th, 2006: Slide: 23/ 30 LEER Z4: Fracture Treatment Fracture Stimulation 1-5: Fluids and Proppants
Sept. 19 th, 2006: Slide: 24/ 30 LEER Z4: Frac 1-4 (5): Fracture Treatments: Friction Results and Fracture Dimensions
Frac 3 Frac 4 Frac 1+2 Sept. 19 th, 2006: Slide: 25/ 30 LEER Z4: Well Cleanout/ Tracer Analysis Result of Fluid Flowback
The Leer Z4 was designed with a mono bore -Cr13-95-completion, which was used during the well simulation and is used as a production string. Fracture initiation was generated in high stress zones, while the fracture propagates into low stress zones, which were generated by lower reservoir pressures. Problem: Fracture stabilization, fracture width and fracture propagation: Risk of pre-mature screenout. Each fracture has been marked by individual tracers. During well cleanout and later production: Quantitative observation on fracture contribution. On the fly-coating with special resin (Expedite XP) prevents backflow of proppants. Sept. 19 th, 2006: Slide: 26/ 30 The scheduled temporary shut-off of stimulated fractures with composite bridge plugs was not possible. As an alternative sand plugs were used to shut-off the prior stimulated perforation Problems: Well head pressure must be kept in the range of 260 300 bar to perform sand cleanout with coiled tubing and to ensure stability of the temporary sand plug. Disadvantage applying high back pressure: critical low fluid velocity (limited hydraulic power) and enhanced erosion on the used 2 coiled tubing. In general: Very limited access to the reservoir. Effective number of perforation holes (3-4). Formation breakdown with fracture initiation: Risk of sand blocks due to residual proppants from prior treatments. LEER Z4: Peculiarities of the Fracture Stimulation
Despite tectonic and facies insecurities: An optimized access of the upper section of the Wustrow-Sandstone was reached. Main contribution of successful geo-stearing was the application of LWD-Tools. During the construction of the well site a gas connection to the public gas network was installed to ensure energy supply to heat-up the fracture fluids. Application of transportable gas-heaters to warm-up the fracture fluids: A quick and flexible heating system was created. Concept: Fracture treatment with mono-bore completed well. No workover after stimulation is needed. The aim is to use the completion during the first production years to reach an economic project. Sirocco gels and Expedite (XP) applied as on the fly - coating was found to be useful. The concept of the fracture treatment was adopted to the local circumstances and improved: General strategy: Data Frac 1, Mini Frac, Data Frac 2 und Main Frac. The well azimuth (about ENE) reached at least a relative low tortuosity friction. Application of individual markers (tracers) were quite successful. On the well location the fracture stimulation team was present during all stages of the treatment. Sept. 19 th, 2006: Slide: 27/ 30 LEER Z4: Positive Experiences
Limited access to the reservoir through generally 3-4 big hole perforations with relatively high initial perforation friction. Problem to maintain fracture width stability during the fracture initiation, especially by fracturing a high stress zone while the fracture propagation will allocate low stress zones. The Mini Frac gel volume must be enhanced significantly to reach about 2/3 of the main fracture height to ensure more Main Frac -treatment-security. This was caused by vertical reservoir pressure changes in the sandstones and thus unexpected vertical stress differences. Due to the dogleg severity and a completion with relatively thick tubing wall the planned composite bridge plugs could not be set. By applying the alternative sand plugs disadvantages occurred: High back-pressure, instable plug settings, additional time loss, insufficient well sandout treatments with coiled tubing (limited circulation rates), higher coiled tubing erosion, formation breakdown with linear gel due to residual sands, risk of sand bridges in the next treatment. For follow-up tight gas projects: Changes in the well path design and the well completion. Sept. 19 th, 2006: Slide: 28/ 30 LEER Z4: Negative Experiences
We like to thank our Leer consortial partner Wintershall AG for the possibility to present this tight gas - contribution. Development of Tight Gas Field with a Multiple Hydraulically Fractured Horizontal Well: Project Leer Z4 Sept. 19th, 2006: Slide: 29/ 30
Picture by: Jan Jeurink Gasbetriebe Emsland Tight Gas Challenges Key Issues: - Knowledge of reservoir characteristics - Horizontal wells in HTHP environment - Stimulation design technologies Sept. 19 th, 2006: Slide: 30/ 30 Development of Tight Gas Field with a Multiple Hydraulically Fractured Horizontal Well: Project Leer Z4